The broad long-term goal of the current research proposal is to gain a deeper understanding of the domaingenerality of cognitive control processes and their underlying neural substrates. The left inferior frontal gyrus (LIFG) has been implicated in mediating resolution of conflict between competing incompatible stimulus representations;however, the extent to which this mechanism functions in a domain-generalfashion is not known. In Experiment 1, fMRI will be used to investigate the extent to which conflict resolutionin verbal and nonverbal domains relies on the same neural substrates, focusing on the LIFG. Subjects willperform three tasks: a lexical ambiguity resolution task, a verbal Stroop task, and a nonverbal Stroop task.The extent of co-localization of neural activity within each participant as well as correlated variation of individual behavioral performance across all three tasks will be investigated. In Experiment 2, we will use a combination of reaction time methods as well as the eye-tracking methodology to test whether similar processing mechanisms are involved in conflict resolution across verbal and nonverbal domains for unimpaired subjects. We also plan to test whether lexical and syntactic ambiguities are resolved via the same processing mechanisms, as suggested by constraint-satisfaction models of language processing. Subjects will perform the tasks used in Experiment 1 as well as a syntactic ambiguity resolution task. Correlated variation in individual performance will be investigated. We will also investigate the contribution of a single nucleotide polymorphism in catechol-O-methyltransferase (COMT), a gene which has been associated with cognitive control, to individual differences in cognitive control abilities. Experiment 3 will address both the questions of the extent of shared neural substrates and the similarity of processing mechanisms involved in conflict resolution across verbal and nonverbal domains. Participants with damage to the LIFG will be tested on the same battery of tasks used in Experiment 1. The voxel-based lesionsymptom mapping methodology will be used to assess the relationship between extent of damage to the LIFG and behavioral deficits in conflict resolution on a voxel-by-voxel basis. The proposed experiments will allow for a comprehensive investigation into the nature of cognitive control mechanisms. Impaired frontal lobe functioning is associated with a number of disorders, including schizophrenia, Alzheimer's Disease, Parkinson's Disease, depression, and anxiety disorders. A greater understanding of the role of prefrontal cortex and the nature of the processing mechanisms involved in mediating conflict resolution across a variety of contexts could better inform treatment strategies for patients.